The present invention relates to a new and improved device for monitoring the yarn travel in the shuttle of a loom, the shuttle being provided with a threader, said device comprising an assembly which includes a piezoelectric transducer element, a yarn feeler member mechanically coupled with the piezoelectric transducer element, an induction coil operatively connected with said transducer element and elastic supporting means. Generally, such a device is intended for stopping the loom when the yarn breaks or ceases to travel on its predetermined path in the shuttle.
U.S. Pat. No. 3,467,149 and Swiss Pat. No. 44l 172 disclose electronic devices for surveying the presence of weft thread in a shuttle loom which comprise a piezoelectric signal generator including a coil and arranged in the shuttle, and a detection circuit including a further coil arranged along the path of the shuttle movement. As shown in said United States patent, the shuttle is formed with a hollow central chamber, within which is mounted a weft bobbin. The weft thread to be supplied by the shuttle is wound about the bobbin and is played out from the front end of the bobbin. The thread passes over the signal generator near the front of the shuttle; and then it leaves the shuttle via an output guide. The bobbin is supported at the rear thereof by means of a bobbin support within the hollow chamber.
The signal generator is mounted within the hollow chamber toward the front thereof by means of rubber bearings which serve to isolate the signal generator from vibratory effects within the shuttle. The signal generator itself includes a base member mounted between the rubber bearings. A wire-like thread feeler element is mounted on the base member and extends to a position such that the weft thread must rub across the feeler element as it is drawn off from the bobbin and moves toward the output guide.
The wire-like thread feeler element is mounted in cantilever fashion at one end to extend upwardly from the base member. The thread feeler element then bends over to extend transversely across and above the base member. The base member, the weft bobbin, and the output guide are all positionally related such that the weft thread presses slightly downwardly upon the thread feeler element toward its free end and rubs across the element during its movement from the bobbin toward the output guide. An elongated piezoelectric crystal is supported at each end thereof by means of mounting elements to extend horizontally above the base member just under the thread feeler element. A vibration coupling member interconnects the thread feeler element and the piezoelectric crystal at a point midway between the two mounting elements.
A signal generator coil is wound about the periphery of the base member. This coil acts as an antenna for controlling electromagnetic field interaction between the moving signal generator and the stationary signal receiver as the shuttle passes closely over the signal receiver. Various other electrical components are embedded within the base member and are electrically connected with the signal generator coil and the piezoelectric crystal.
In said United States and Swiss patents no details are disclosed about the disturbances influencing the piezoelectric signal generator from outside the shuttle, and the enormous accelerations the shuttle undergoes when the loom is working and which imply very serious problems. This refers particularly to the impacts acting upon the shuttle when driven or stroken by the picker, further to the intense noise existing in weaving sheds, and to the vibrations generated by the operating loom which may be transferred to the shuttle. By such influences the signal generator may be damaged or even rendered inoperative, or wrong electrical signals may be generated in the sensitive signal generator or other components of the monitoring equipment which cause unwanted stops of the loom.
A further problem results from spurious electrical signals from the surroundings of the loom or the electric supply which may cause trouble by inductive effects on the induction coils of the signal generator and detecting circuit arranged at the loom.
A further rather difficult problem is the arrangement and accommodation of the signal generator in the front end of a conventional weaving shuttle without adding to the dimensions of the shuttle. Any enlargement of the width, height and/or length of the shuttle might necessitate structural changes on the loom and thus would be impracticable.